Originally posted by MJB DIGITAL Well I learned in the last thread that the time of exposure isnt changed by the size of the format.
But I do know that the DOF is thinner.
So if you were shooting a bit longer of a focal length--in available light--and you needed to open up your lens to a wider aperture, you might have too thin of DOF....
is that right?
"It is right" depends on what assumptions you are making when drawing the comparison.
If you stand 10ft from the subject with a 50mm lens and aperture at f/8:
- APS-C gives you a DOF of 39" and FOV of 68"
- 135 (full-frame) gives you a DOF of 62" and FOV of 104"
However and this is where the "DOF is thinner with full-frame" argument lies...
If you use a 50mm lens and aperture of f/8 and frame your shot so you have a 6ft (72") FOV:
- With APS-C you'll be standing 129in (10ft9in) from subject and have a DOF of 45.5".
- With 135 you'll be standing 7ft (84in) from subject and have a DOF of 29.5". To remain at 10.75ft from subject you'd need a 77mm lens to achieve the same FOV at f/8 and your DOF would drop to 28.8".
The argument is not wrong, it simply rarely gets explained fully.